The present invention relates to an electrocardiograph computer display system, particularly adapted for the visual display and automatic processing of large volumes of electrocardiac signals and enabling the permanent recording and analysis of such signals in a relatively short period of time.
Electrical signals that appear at a person's skin as a result of the electrical activity of the heart are known as ECG signals. These ECG signals exhibit particular wave forms which correspond to the action of the heart muscle and reflects both in timing and in character the condition of the heart. It is well-known to place electrodes on the patient's skin to sense the ECG signals and to present them for visual analysis, either in real time or in a subsequent time for use by physician is the analysis over an extended period of time of a continuous ECG signal which reflects heart activity during the normal activities of the patient and which displays anomalous heart signals which represent arrhythmic and ectopic activity. As used herein arrhythmic heart activity includes activity which is abnormal, such as irregular variations in rhythm and ectopic activities, such as premature ventricular contractions, ventricular ectopic beats, and supra ventricular ectopic beats. More especially, it is desired to accumulate and analyze large volumes of such ECG signals during normal activities of the patient, as for example, over a twenty-four hour period, and to review this accumulation in a highly accelerated mode using a visual display to determine the frequency and character of the various heart signals and to identify those which are of particular interest. For this purpose there are known systems which accomplish the foregoing by recording the ECG signals in real time on a small compact tape recorder, which is worn by the patient. The recording signals are then processed by replaying the same at a much faster speed with a displayer presentation of the signals on a cathode ray oscilloscope in which each ECG complex is superimposed on predecessor complexes. This type of display is known as an AVSEP display and the description of such is set forth in U.S. Pat. No. 3,215,136 issued Nov. 2, 1965 in the name of Norman J. Holter, et al. The scanning device of U.S. Pat. No. 3,215,136 utilizes superimposition of the ECG signals from two different tracks of a magnetic recording tape. In playback the signal from one track was used to trigger an oscilloscope trace of the signal from the other track. Oscilloscope screen persistance permitted the superimposition of successive signal complexes. A subsequent improvement is set forth in U.S. Pat. No. 3,718,772 issued Feb. 27, 1963 in the name of Clifford Sanctuary which provides for the use of a single track magnetic tape recorder wherein trigger signals are produced by a separate trigger head scanning a single track of the magnetic tape recording. U.S. Pat. No. 4,157,571 issued June 5, 1979 to Stephen K. Shu discloses an improved scanner in which the tape is received at high speed by an operator, who is also able to stop the display and initiate real time, single frame viewing modes in which a segment of tape is repeated, an interval of the signal thereon representing a frame stored in a digital memory, thus the content of memory can be displayed in real time for analysis by the operator and a selected print-out can be obtained as desired.
The various display systems set forth in the above referenced patents include recording the same ECG signal on two tracks of a recording and developing a trigger signal from the rising edge of the R wave from the one track in order to trigger the signal of the other track. Generally, a time separation between the trigger signal and the signal to be displayed, representing in advance, has been found to be about 200 milliseconds for satisfactory results. Based on this system the ECG signals can be superimposed one on top of the other to provide visual comparison between the wave shapes of successive signals.
It is also known to analyze successive ECG signals to determine the R to R interval between successive pulses and to present the succession of R to R intervals as a bar graph which has come to be known as an ARRHYTHMIAGRAPH in general, the bar graph will visually indicate changes in the R to R spacing which changes are directly correlateable to PVC occurrences and other abnormalities. The use of the ARRHYTHMIAGRAPH and an audio presentation of the ARRHYTHMIAGRAPH simultaneously with viewing of the superimposed ECG signals has been found to be particularly effective way in which the SCAN recordings of ECG activity in a rapid manner. This type of scanning has become known as AVSEP. One known scanning system has combined two channels of ECG or AVSEP signal with an arrhythmiagraph in a single tube. However, even though delay lines or shift registers have been used to supply the triggering pulses, there nevertheless has been required the use of two playback heads per channel and the employment of a three gun CRT tube in order to obtain the simultaneous presentation of both channels of ECG and ARRHYTHMIAGRAPH.
Further changes have been made in which a single channel of ECG has been used to obtain a single channel AVSEP by employing a one-shot multi-vibrator as a triggering circuit and displaying the video signal after passing the same through a delay circuit such as an analog or digital shift register. Even so, such a system has required the presentation of simultaneous ARRHYTHMIAGRAPH on a separate tube which is visually difficult for the operator. Reference is also made to U.S. Pat. No. 4,073,011 to Isaac R. Cherry and Donald L. Anderson entitled Electrocardiographic Computer.
The general scheme of analysis set forth in all these references calls for the playback to include two portions. The first portion is an AVSEP and ARRHYTHMIAGRAPH display which is presented to the operator or physician. The purpose of such presentation is to identify those occurences in ECG signal which it is desired to investigate more fully as an assist in obtaining such an analysis, computers have been devised to characterize the wave shape of such successive signals and to automatically stop the AVSEP/ARRHYTHMIAGRAPH display for time stationary analysis. Among the disadvantages of the prior art systems include the need for multiple head playback arrangements, the use of analog and digital delay lines for processing of ECG signals, the requirement of multi-gun CRT display scopes, the inability to present within a single visual field all of the information required by the operator and an inability to relate time stationary ECG displays to each other and to the AVSEP/ARRHYTHMIAGRAPH SCAN.